This invention relates to the polymerization of olefins using large pore crystalline catalysts to produce poly-olefins characterized by low volatility and excellent viscometic properties.
Poly-alpha-olefins are highly useful as basestocks for functional fluids such as lubricants, transmission fluids, and transformer fluids. Poly-alpha-olefins are conventionally prepared by the polymerization of alpha-olefins using a Friedel-Crafts catalyst such as BF3 or AlCl3. The poly-alpha-olefin typically is then hydrogenated to stabilize the polymer against oxidation and degradation.
In a typical poly-alpha-olefin production process, 1-decene is used as the starting material (see, e.g., U.S. Pat. Nos. 3,742,082 and 4,282,392). Polymers of 1-decene and mixtures of 1-decene with 1-octene and/or 1-dodecene generally result in base fluids having a high viscosity index (VI) and low pour point. 1-decene and other linear alpha-olefins are made from ethylene. The polymerization of ethylene usually produces a wide range of alpha-olefins, from 1-butene to 1-C20 and higher alpha-olefins, with the product distribution governed by the degree of polymerization. The higher alpha-olefins, such as C14 or higher, generally are not used as starting materials for poly-alpha-olefin production because the resulting polymers typically have undesireable properties such as high pour point and high volatility that render them unsuitable for use as high performance functional fluids (see James A. Brennan, Wide-Temperature Range Synthetic Hydrocarbon Fluids, IND. ENG. CHEM. PROD. RES. DEV., 19, 2-6 (1980)). Accordingly, current poly-alpha-olefin manufacturing processes generally use lower alpha olefins, such as C8, C10, and C12 alpha-olefins, as starting materials without taking advantage of the remaining higher olefins produced in the production facilities. The following is a summary of some of the prior art in this field of invention:
U.S. Pat. No. 4,218,330 discloses a process for oligomerizing higher olefins such as C12-18 with cationic catalysts, such as boron trifluoride, to form lubricant products.
U.S. Pat. No.3,322,848 discloses a method of manufacturing lubricating oils from C10 to C18 alpha olefins using a catalytic agent prepared by base exchanging a crystalline alkali metal aluminosilicate having uniform pore openings of 6 to 15 Angstrom units with an ionizable metal compound, such as rare earth metals. This process generally resulted in low lube yields and significant amount of coke formation. Furthermore, the products made from 1-dodecene or 1-tetradecene had relatively high pour points.
U.S. Pat. No. 4,547,613 discloses the conversion of olefins by contact with a ZSM-5 type zeolite catalyst that has been conditioned by a previous contact with a light olefin preferably of three to six carbon atoms per molecule.
U.S. Pat. No. 4,517,399 discloses the conversion of C3 to C18 olefins over a ZSM-5 type catalyst to obtain a lube oil with an enhanced viscosity index. The active catalytic centers of the ZSM-5 type catalysts disclosed in this patent are located inside small and restricted channels having openings usually smaller than 5.6 Angstroms throughout the zeolite structures. These small pores impose little or no restriction for the smaller olefins, such as C2, C3, and C4 olefins to diffuse to the active sites inside the zeolite channels and polymerize to give lube molecules with high efficiency. However, these zeolites with small and restricted channels are not very effective for conversion of large olefins into polymers because the large olefins diffuse very slowly along the small and restricted channels. Prior art attempts to drive the reaction by raising the reaction temperature or using prolonged reaction times lead to undesirable side reactions, such as double bond isomerization, skeletal isomerization, and cracking, that, in turn, decrease desirable product yields. Examples of such attempts and the accompanying side reactions are described in U.S. Pat. No. 5,523,511 (skeletal isomerization) and WO 92117 (isomerization of 1-olefins into internal olefins).
In accordance with the present invention, novel processes have now been discovered that can produce poly-olefins from olefins, and particularly from higher olefins such as C14 and higher, using catalysts with widely open structures and having high activity for polymerization. In preferred embodiments, the novel processes of the invention utilize crystalline catalysts having constraint indices of less than about three. The resulting poly-olefins have excellent pour point, volatility and viscometric characteristics, especially when compared to poly-olefins produced from conventional catalysts, such as Friedel Crafts catalysts. In addition, these processes enable the use of higher olefins as starting material for poly-olefin manufacturing, thereby easing the demand for 1-decene as a feedstock.
The present invention provides processes for polymerizing an olefin, preferably an alpha-olefin, having from about 8 to about 30 carbon atoms. The processes utilize large pore crystalline catalysts having constraint indices of less than about three to produce poly-olefins that exhibit low viscosity and low volatility. In particular, the catalysts of the present invention provide for the use of higher olefins, such as C14, C16, C18 or higher, in poly-olefin production processes.
The poly-olefins produced in accordance with the novel processes of the present invention have desirable viscosity, volatility, and pour point characteristics. In particular, the polymers of the present invention that are formed from higher alpha-olefins, such as C14 to C18, exhibit unexpected properties, especially when compared to conventional poly-alpha-olefins formed from C8 to C12 olefins.